<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
   /* float:  
   calc(100% - 左右宽度和) */

        div {
           overflow: hidden;
        }
      header {
        float: left;
        width: 200px;
        height: 100vh;
        background-color:rgb(201, 159, 105) ;
      }
      aside {
        float: left;
        width:calc(100% - 400px);
        height: 100vh;
        background-color: blanchedalmond;
      }
      footer {
        float: left;
        width: 200px;
        height: 100vh;
        background-color: burlywood;
      }
    </style>
  </head>
  <body>
    <div>
      <header></header>
      <aside></aside>
      <footer></footer>
    </div>
  </body>
</html>